Bug 1014466 - Part 1: Only send readystatechange event when state changed. r=khuey

dom/workers/XMLHttpRequest.cpp

@@ -1669,7 +1669,12 @@ XMLHttpRequest::MaybeDispatchPrematureAbortEvents(ErrorResult& aRv)
   mWorkerPrivate->AssertIsOnWorkerThread();
   MOZ_ASSERT(mProxy);
 
-  mStateData.mReadyState = 4;
+  // Only send readystatechange event when state changed.
+  bool isStateChanged = false;
+  if (mStateData.mReadyState != 4) {
+    isStateChanged = true;
+    mStateData.mReadyState = 4;
+  }
 
   if (mProxy->mSeenUploadLoadStart) {
     MOZ_ASSERT(mUpload);
@@ -1690,10 +1695,12 @@ XMLHttpRequest::MaybeDispatchPrematureAbortEvents(ErrorResult& aRv)
   }
 
   if (mProxy->mSeenLoadStart) {
-    DispatchPrematureAbortEvent(this, NS_LITERAL_STRING("readystatechange"),
-                                false, aRv);
-    if (aRv.Failed()) {
-      return;
+    if (isStateChanged) {
+      DispatchPrematureAbortEvent(this, NS_LITERAL_STRING("readystatechange"),
+                                  false, aRv);
+      if (aRv.Failed()) {
+        return;
+      }
     }
 
     DispatchPrematureAbortEvent(this, NS_LITERAL_STRING("abort"), false, aRv);